AR15/ M4 Upper Receiver Build

We’ve been getting a lot of requests to build what we would consider a good general purpose AR15 upper receiver. With a focus on durability, reliability and ease of maintenance this is what we came up with, our own M4gery!

Equipped with a cold hammer forged chrome lined Daniel Defense M4 contour barrel and a carbine length gas system, parts for this upper will be easy to find down the line. Coupled with the Lite Rail 9.5 FSP, the shooter will have a similar firing grip to a mid length gun. The CSAT and tritium iron sights provide the shooter to engage point targets up close, as well as distant targets without changing his stock weld. The 2MOA Aimpoint T1 similarly provides a rapid aiming solution for up close targets, while providing a refined aiming point for far engagements while the Surefire Mini Scout Slight provides the ability to illuminate targets in low light conditions.

Compliment this upper with your collapsible stock lower, and you are ready to roll!

We selected a Daniel Defense stripped 16″ M4 style upper receiver to build on. With a cold hammer forged barrel and gas tube installed on an A4 upper, it provides a good starting point for most builds. The forward assist and ejection port cover are already in place and you can’t argue with the price point.Since we are installing a new Daniel Defense Lite Rail 9.5 FSP with its own barrel nut and bolt up plate, the orginal barrel nut will have to be removed. To do this we will need to remove everything forward of the barrel nut from the barrel. With a roll pin punch we remove the gas tube pin by drifting it out of place.With the gas tube pin removed, the gas tube can be slid out of the front sight assembly.Placing the upper receiver in a set of vise blocks from our critical tools kit, we use our armorers wrench (also from the kit) to remove the flash hider by turning it counter clockwise. Before doing so, we make a witness mark on the flash hider to make indexing easier upon reinstallation.Using our front sight bench block, we secure the front sight assembly to facilitate removal of the taper pins. Note: Notice we reinserted the gas tube roll pin into the assembly so it does not get lost.Using a steel punch, we drift the taper pins out of the base. The block is clearing labeled “pins out” to prevent the user from inadvertently driving the pins in the wrong direction.Once again we secure the upper in the vise blocks. This time to remove the barrel nut.With the armorers wrench firmly seated in place, we can turn the wrench counter clockwise to remove it.To install our rail system we removed these items. The front sight base assembly, taper pins, flash hider, crush washer, hand guard cap, gas tube (not shown) and gas tube roll pin (not shown) will be reused.The AR15 Lite Rail bolt-up plate and barrel nut are placed onto the barrel. The counter bored face of the bolt-up is left facing the muzzle. We ensure that the gas tube hole is aligned with the hole in the receiver.The Daniel Defense Lite Rail barrel nut wrench is specifically made to install the Lite rail. The wrench works with a 1/2″ drive torque wrench.The barrel nut is torqued to 50 foot pounds.The AR15 Lite Rail is slid onto the barrel against the bolt-up plate. Two screws are inserted into the bottom holes on each side and hand tightened.The rail is aligned with the receiver and the rest of the screws are installed. The center, bottom and finally top screws are tightened. We like to use a QD mount, in this case a GGG, to keep everything aligned.We now reattach the gas tube to the front sight base by reinserting it into the front sight assembly and driving in the gas tube pin with a roll pin punch.The front sight is slid onto the barrel, we make sure the gas tube passes through the upper receiver. The two taper pins are carefully driven in through the openings in the Lite Rail with a brass drift.With the upper held securely in vise blocks, the flash hider is reattached. Since we made a witness mark earlier, we merely line the two marks up with the armorers wrench.We are huge fans of the CSAT rear sight. We find the Larue LT103 QD fixed BUIS is an excellent platform as well. We had an extra Larue BUIS lying around and decided to reuse it for this upper.To installed the CSAT rear into the Larue BUIS, we begin by using an allen key to remove the set screws from the front of the sight assembly. The first screw needs to be removed, the second one behind it, merely needs to be loosened.Once the set screw is loose, the windage mechanism is simply unscrewed from the original rear sight aperture Notice the ball detent underneath it. Make sure you do not lose this ball or the spring behind it.The windage adjustment screw is simply threaded back onto the CSAT rear. By pressing on on the outside of the adjustment screw, you can tighten the first, then second set screws which will in turn hold the windage screw in place. Once all the pieces are back together, we mechanically zero the rear sight.We selected an XS white stripe tritium front sight for this upper. Using the A1/A2 sight tool (left, right is the supplied model which is harder to use) we simply replace the front sight by unscrewing the old one and installing the new one.Having long been fans of the 4MOA T1, we selected the new 2MOA T1 for this upper. Subtending 4″ at 200 yards, more accurate shooting should be possible at distance. To install the sight on the QD mount, we remove the four screws on the factory supplied base assembly.The QD LT660 base is a Rifleshooter.com favorite and is available from Brownells. Simply install the four cap screws into the bottom of the sight. Remember, the T1 has an aluminum housing, be careful not to over-tighten and strip the screws.A Surefire M300A Mini Scout light is installed on the left side of the rail. We prefer the rear push button function, the light is also supplied with a pressure pad.

Dropping in a charging handle and Daniel Defense chrome bolt carrier group and we are ready to go! Range report to follow!

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